Monolithic ceramic attachment bushing incorporated into a ceramic matrix composite component and related method

ABSTRACT

12 A high temperature gas turbine component includes an inner core made of a monolithic ceramic material embedded within an outer CMC shell. The inner core may be formed with a through hole, blind hole, wear pads and the like. A method of making the bushing includes the steps of a) forming an inner core of silicon nitride or silicon carbide; and b) applying a ceramic matrix composite material over substantially all of the inner core.

BACKGROUND OF THE INVENTION

[0001] This invention relates to ceramic matrix composite components in general, and specifically, to a high temperature ceramic matrix composite component that incorporates a monolithic attachment bushing.

[0002] Ceramic matrix composites (CMC's) offer high material temperature capability. In the gas turbine field, however, CMC components often require attachment to, or engagement with, lower temperature metallic gas turbine components. Problems associated with the attachment of known silicon carbide ceramic matrix composites (CMC's) to metallic components include wear, oxidation (due to ionic transfer with metal), stress concentration (from clamping loads), transition to thick section fabrication, and fiber damage in creating holes in the CMC's.

SUMMARY OF THE INVENTION

[0003] In an exemplary embodiment of the invention, advantage is taken of the very high strength of monolithic ceramics to absorb the clamping loads of bolt and pin-type attachment means. The CMC component thus has an inner core made of either silicon carbide or silicon nitride monolithic ceramic that is embedded within an outer CMC shell. It is understood that material selection for the inner core depends on specific attachment requirements, and the shape of the inner core of the bushing could be any number of shapes, several of which are disclosed herein. Preferably, the shape of the inner core would thus be optimized to insure that the inner core is well encased within the outer CMC shell, and that the load is optimally distributed into the CMC component structure. In one exemplary embodiment, the required size of a through hole in the inner core of the bushing will contribute to set the overall size of the bushing in order to preserve an appropriate surface area of monolithic ceramic within the outer CMC shell.

[0004] In other embodiments, the through hole may be eliminated in favor of a blind hole, or even a solid center with oppositely facing wear surfaces.

[0005] The CMC shell that incorporates the bushing may be any gas turbine or other component, and is not limited to the shape or configuration described and/or illustrated herein.

[0006] Accordingly, in its broader aspects, the present invention relates to a turbine component comprising an inner core comprised of a monolithic ceramic material having a through-hole formed therein of predetermined diameter, the inner core encased within an outer shell composed of CMC material.

[0007] In another aspect, the invention relates to a gas turbine component comprising an inner core made of silicon nitride or silicon carbide, the inner core having a first outer diameter and a through-hole formed therein having a second diameter, the first diameter being 2.5 4 times the second diameter; wherein the inner core is enclosed within an outer shell of ceramic matrix composite material.

[0008] In another aspect, the invention relates to a gas turbine component including an inner core of silicon nitride or silicon carbide material, the inner core substantially encased within an outer shell composed of CMC material.

[0009] In still another aspect, the invention relates to a method of making a gas turbine component comprising a) forming an inner core of silicon nitride or silicon carbide; and b) applying a ceramic matrix composite material over substantially all of the inner core.

BRIEF DESCRIPTION OF DRAWINGS

[0010]FIG. 1 is a side elevation of a component having a monolithic ceramic core bushing encased within a ceramic matrix composite material in accordance with an exemplary embodiment of the invention;

[0011]FIG. 2 is a side section view of the component shown in FIG. 1;

[0012]FIG. 3 is a side section view of a component in accordance with an alternative embodiment of the invention;

[0013]FIG. 4 is a side section view of a component in accordance with another embodiment of the invention;

[0014]FIG. 5 is a side section view of a component in accordance with another embodiment of the invention; and

[0015]FIG. 6 is a side section view of a component in accordance with still another embodiment of the invention.

DETAILED DESCRIPTION

[0016] With reference to FIGS. 1 and 2, a gas turbine component 10 includes a monolithic ceramic inner core 12 made of either silicon nitride or silicon carbide embedded within an outer CMC shell. The silicon nitride or silicon carbide bond well with the surrounding CMC shell, while providing extremely hard and wear resistant surfaces. Monolithic ceramics also can maintain close tolerances needed for specific attachment requirements. In this embodiment, the inner core 12 includes a through-hole 14 that is sized to receive another gas turbine component such as a metal bolt shank or pin. The inner core 12 also includes flat, annular portions or faces 16, 18 that may or may not be flush with the opposite sides 20, 22 of the outer CMC shell 24, depending on the particular attachment design needed between the metallic and composite structures.

[0017] The inner core 12 is reduced in thickness in a radially outward direction in symmetrical fashion from the flat annular faces 16, 18 to an internal, maximum diameter curved edge 26 via substantially flat tapered surfaces 28, 30. Edge 26 is substantially centered between the sides 20, 22 of the CMC shell 24.

[0018] In an alternative embodiment shown in FIG. 3, where similar reference numerals for corresponding elements are used, but with the prefix “1” added, the inner core 112 of the component 110 reduces in thickness in a radially outward direction from the flat annular faces 116, 118 to an internal, maximum diameter convex curved edge 126 via concave curved surfaces 128, 130.

[0019] The arrangement described above is intended to take advantage of the very high strength of monolithic ceramics to absorb the clamping loads of bolt and pin type attachments. The inner core 12 allows the stress field around attachment points to be spread out over a larger area supported by the surrounding fibers within the larger area CMC shell 24.

[0020] Material selection will depend on specific applications, and the shape of the inner core 12 of the bushing may be varied to provide optimum load distribution into the surrounding CMC shell 24. In addition, the diameter of the hole 14 determines in part the size of the bushing in order to preserve an approximate surface area of the monolithic inner core within the CMC shell. Preferably, a ratio of overall monolithic inner core diameter to hole diameter of 2.5 4 is maintained, the exact ratio being determined by specific application requirements.

[0021]FIG. 4 illustrates another embodiment where an inner monolithic core 32 of silicon nitride or silicon carbide is embedded within an outer CMC shell 34. Here, the inner core 32 is formed with radial flanges 36, 38 on opposite sides of the core, and a through hole 40. The inner core 32 is substantially completely encased within the outer shell 34, the latter having drilled (or otherwise formed) ends 42, 44 that are aligned with the through hole 40. Thus, the through hole is recessed relative to the side surfaces 46, 48 of the component.

[0022]FIG. 5 illustrates yet another embodiment where the monolithic inner core 50 of silicon nitride or silicon carbide is formed substantially as a solid disk with beveled radially outer edges 52, 54, with a blind hole 56 drilled (or otherwise formed) in the core. Blind hole 56 is aligned with a drilled (or otherwise formed) hole 58 in the outer CMC shell 60. The core 50 is otherwise completely encased within the outer shell 60.

[0023]FIG. 6 illustrates yet another embodiment of the invention where an inner core 62 substantially similar to inner core 50 (FIG. 5), but without the presence of a blind hole. In this embodiment, raised wear pads 64, 66 are formed on opposite sides of the inner core and substantially centered thereon. The outer shell 68 is applied such that only the wear pads 64, 66 are exposed, the remainder of the core encased within the outer shell 68.

[0024] It will be appreciated that the through holes, blind holes or wear pads may be flush or recessed with respect to the outer CMC shell. In other instances, the inner core and/or wear pads may project beyond the outer CMC shell. It will further be appreciated that the CMC outer shell may take on any shape, as dictated by the particular gas turbine component. In other words, the CMC outer shell may be a motor casing, a bearing stand, or any other component otherwise advantageously formed of CMC composite material.

[0025] In each case, the manufacture of the gas turbine component is similar. Thus, after producing the silicon nitride or silicon carbide monolithic inner core (12, 112, 32, 50 or 62), the outer CMC shell (24, 124, 34, 60 or 68) is fabricated over and/or around the inner core. The manner in which this is done may be similar to the way in which components are embedded in fiberglass, with layer upon layer of the CMC laid up on the monolithic inner core in sections or strips, until the outer dimensions of the component are achieved.

[0026] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

1. A turbine component comprising: an inner core comprised of a monolithic ceramic material having a through-hole formed therein of predetermined diameter, said inner core encased within an outer shell composed of CMC material.
 2. The turbine component of claim 1 wherein said monolithic ceramic material comprises silicon nitride.
 3. The turbine component of claim 1 wherein said monolithic ceramic material comprises silicon carbide.
 4. The turbine component of claim 1 wherein said inner core has front and rear faces about said through-hole that are flush with opposite sides of the outer shell.
 5. The turbine component of claim 1 wherein said through hole in said inner core is recessed relative to opposite sides of the outer shell.
 6. The turbine component of claim 4 wherein said inner core further includes surfaces that taper inwardly from said front and rear face portions to a curved, radially outer edge centered relative to said opposite sides of said outer shell.
 7. The turbine component of claim 6 wherein said surfaces are substantially flat.
 8. The turbine component of claim 6 wherein said surfaces are concave.
 9. The turbine component of claim 1 wherein said outer shell is molded around said inner core.
 10. The CMC component of claim 6 wherein said maximum diameter of said inner core is between 2.5 and 4 times said diameter of said through-hole.
 11. A gas turbine component comprising an inner core made of silicon nitride or silicon carbide, said inner core having a first outer diameter and a through-hole formed therein having a second diameter, said first diameter being 2.5 4 times said second diameter; wherein said inner core is enclosed within an outer shell of ceramic matrix composite material.
 12. The gas turbine component of claim 11 wherein said inner core has front and rear faces about said through-hole that are flush with opposite sides of said outer shell.
 13. The gas turbine component of claim 12 wherein said inner core further includes surfaces that taper inwardly from said front and rear faces to a radially outer edge substantially centered relative to said opposite sides of said outer shell.
 14. The gas turbine component of claim 13 wherein said surfaces are substantially flat.
 15. The gas turbine component of claim 13 wherein said surfaces are concave.
 16. A gas turbine component including an inner core of silicon nitride or silicon carbide material, said inner core substantially encased within an outer shell component of CMC material.
 17. The gas turbine component of claim 16 wherein said inner core is formed with as through hole, opposite ends of which are flush with respective opposite sides of said outer shell.
 18. The gas turbine of claim 16 wherein said inner core is formed with a through hole, opposite ends of which are recessed relative to respective opposite sides of said outer shell.
 19. The gas turbine of claim 16 wherein said inner core is formed with raised wear pads that are exposed on respective opposite sides of said outer shell.
 20. The gas turbine component of claim 1 6 wherein one side of said inner core is formed with a blind hole.
 21. The gas turbine component of claim 20 wherein said blind hole is recessed to one side of said inner core.
 22. A method of making a gas turbine component comprising: a) forming an inner core of silicon nitride or silicon carbide; and b) applying a ceramic matrix composite material over substantially all of said inner core.
 23. The method of claim 22 wherein in step a) said inner core is annular and formed with a hole of predetermined diameter, diameter that is 2.5 4 times larger than said hole diameter.
 24. The method of claim 23 wherein said inner core is formed to include flat front and rear faces connected to a radially outer edge by tapered surfaces.
 25. The method of claim 24 wherein said tapered surfaces are substantially flat.
 26. The method of claim 24 wherein said tapered surfaces are concave.
 27. The method of claim 24 wherein, during step b), said ceramic composite matrix material is applied in such a way that all of said inner core is covered except for said flat front and rear faces.
 28. The method of claim 22 wherein said inner core is formed with a blind hole.
 29. The method of claim 22 wherein said inner core is formed with one or more wear pads that remain exposed after step b). 